Injection device

ABSTRACT

A pen injection device designed for use with dual or multi-chamber cartridges (14), is provided with an extended length plunger (24) having a non-drive portion (24′) on its forward end and the usual screw-threaded drive portion (24′) on its rearward end. This arrangement allows the plunger to be pushed forwardly whilst the dosing drive mechanism is disengaged to effect a reconstitution movement of the rearward bung (18′) in the cartridge. Thereafter the threaded portion on the plunger (24′) engages the drive mechanism to allow metered dosing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an injection device and in particular, but notexclusively, to an injection device for use with dual or multi-chambercartridges.

2. Description of the Related Art

In typical dual chamber cartridges two spaced bungs are disposed withinthe cartridge to define two separate chambers, for example a forwardchamber containing lyophilised powder and a rearward chamber containingdiluent liquid. A bypass channel in the cartridge wall provides a bypasspath between the two chambers, but is initially closed by the presenceof the forward bung. In use, as pressure is applied to the rearward bungto move it, the liquid in the diluent chamber and the forward bung movetogether forwardly and in doing so uncover the bypass channel so thatthe fluid from the diluent chamber flows into the forward chamber to mixwith the lyophilised powder. The forward bung and the rearward bung maybe of similar form or the forward item may be in the form of a moveablewall.

In such cartridges, it will be appreciated that two phases of movementof the rearward bung are required, namely a first, reconstitution phaseduring which the rearward bung moves to move the liquid in the rearwardchamber forward to mix with the material in the forward chamber, and asecond, dosing phase during which metered movement of the rearward bungis required to expel a preset dose.

In a typical pen injector such as our AUTOPEN® device, the pen injectorcomprises a main body housing the pen injector mechanism which screwsinto a cartridge holder which holds the cartridge of therapeuticsubstance. In use the user dials in a required number of units dosage ona dose selector on the body and then presses the release button whichcauses an internal plunger in the body in contact with the bung toadvance it by the required amount to expel a corresponding dose from thecartridge in the cartridge holder.

A problem arises in relation to such devices in relation to use withdual chamber cartridges because the amount of movement required duringthe reconstitution phase 15-20 mm or more is much greater than thatrequired for the doses (typically 0.1 to 0.2 mm per unit dose). If thepen injector mechanism were to be used to try and achieve the length ofstroke required for the reconstitution phase this would be extremelytedious requiring many cycles of repetitive dialling in and firing. Aprevious attempt to overcome this problem provided an pen injector inwhich the body and the cartridge holder had extended threaded matingsections so that the holder could be engaged with the body and screwedcontinuously until the plunger had driven the rearward bung by an amountsufficient for the reconstitution phase. Thereafter the pen injectormechanism could be operated as required to effect a series of doses.This extended screw thread arrangement is also extremely tedious andtime consuming.

There is therefore a need for an injection device for use with amulti-chamber cartridge, to allow convenient reconstitution followed bythe usual dose metering in successive injections.

BRIEF SUMMARY OF THE INVENTION

Accordingly, this invention provides an injection device for dispensingin use a substance from a dual or multi-chamber cartridge, saidcartridge having a bung moveable in a first, reconstitution, extent ofmovement and a second, dosing, extent of movement (which may bevariable), said device comprising:

a body portion;

a plunger mounted in said body portion for longitudinal movement withrespect thereto in a forward dispensing direction to co-operate in usewith said bung;

a plunger drive element disposed adjacent said plunger for driving saidplunger;

said plunger having a drive portion adapted to mate with a complementarydrive portion on said plunger drive element and adapted to impart dosingmovement to said plunger;

said drive portion extending only partly along said plunger to leave aforward non-drive portion;

whereby, during a reconstitution phase, said plunger may be movedlongitudinally forwards from a position with the non-drive portionadjacent said plunger drive element, to bring its drive portion intodriving engagement with the drive portion on said plunger drive element.

In this manner, the plunger may be moved to effect reconstitution of thetherapeutic mixture in the cartridge before the drive portions areengaged. This allows a separate reconstitution movement followed by ametered dosing movement of the plunger, without compromising therequirements of either movement.

Preferably, said drive portions on said drive element and said plungerare complementary threaded drive portions. Thus the plunger may carry amale thread and the drive element may include a bore having a femalethread therein although the reverse is not excluded. In this instance,the non-drive portion of said plunger may comprise a non-threadedportion sized to be moveable freely through the drive element until thedrive portions engage.

The initial reconstitution movement of the plunger may be achieved invarious ways. In one arrangement a mover element is slideably moveablein said body portion and has an externally accessible push region sothat the element may be manually pushed to engage said plunger and tomove it longitudinally until said complementary drive portions are indriving engagement. The device preferably includes means for releasablypreventing longitudinal movement of said mover element. This maytypically comprise a bayonet type lock arrangement between the moverelement and an element fixed with respect to the body portion. Inaddition, or alternatively, it may comprise a releasable spacer element.

Conveniently, the mover element includes a cap element defining the pushregion, said cap element being adapted to engage in snap engagement inan end region of said injection device.

Preferably, the device includes bias means for urging the plungerelement towards complementary driving engagement with said driveelement. Said bias means and said plunger are preferably arranged suchthat said plunger is isolated from the influence of the bias means apreset distance after initial driving engagement between saidcomplementary drive portions.

The drive to the drive element may be achieved in various ways and inone embodiment, it is in the form of a drive mechanism which applies apre-selectable amount of angular movement to said drive element onactivation thereof. Thus the drive mechanism may comprise a usersettable dose setting member rotatably mounted on said body portion toset a dose, with a spring acting between the dose setting member and thebody portion, said spring being strained to a variable extent dependingon movement of said dose setting member. A ratchet arrangement may bedisposed between the dose setting member and said drive element,allowing one way relative movement therebetween as the dose settingmember is rotated to set a dose. A trigger member may be provided toprevent rotary movement of the drive element during the dose settingroutine but to be releasable thereafter to allow said spring to rotatesaid dose setting member and said drive element in unison by an amountcorresponding to the set dose. In this arrangement, the dose settingelement preferably includes a generally cylindrical portion surroundingat least part of the plunger.

The dose setting element may conveniently comprise a rotatable collar orthe like on the rearward end of the injection device and, whereprovided, the mover element may be arranged to snap fit into said collarwhen the mover element is moved fully forward.

Whilst the invention has been described above, it extends to anyinventive combination of the features set out above or in the followingdescription.

BRIEF DESCRIPTION OF VIEWS OF THE DRAWINGS

The invention may be formed in various ways, and an embodiment thereofwill now be described by way of example only, reference being made tothe accompanying drawings in which:

FIG. 1 a is a schematic view of a pen injection device in accordancewith this invention for use with a multi-chamber cartridge, beforereconstitution;

FIG. 1 b is an expanded view of the ratchet mechanism;

FIG. 2 is a schematic view similar to FIG. 1 a but during the latterstages of reconstitution and before a dose has been set, and

FIG. 3 is a schematic side view after a number of doses have beenexpelled.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, a pen injection device is made up of a cartridge holder10 screw-threaded onto a main body portion 12. Within the cartridgeholder 10 is provided a dual chamber cartridge 14 having two chambers16′ and 16″ defined by rearward and forward bungs 18′, 18″. The rearwardchamber 16′ normally contains a diluent liquid and the forward chamber16″ normally contains a lyophilised powder. Part way along the syringe,and initially closed off by the forward bung 18″, is a bypass 20 channeldisposed in the wall of the cartridge and interconnecting the forwardand rearward chambers 16′, 16″. Screwed onto the end of the cartridgeholder 10 is a double ended needle 22 which pierces a rubber membrane(not shown) in the front of the cartridge.

The rearward bung 18′ in use is acted upon and driven by a plunger 24.The plunger 24 can move linearly under certain conditions but isprevented from rotation by means of two diametrically opposed channels(not shown) which cooperate with a correspondingly shaped washer 26itself held against rotation on the forward end of the main body portion12. Unlike previous such devices, in which the plunger shaft has beenthreaded along its operational length, in this embodiment of theinvention the forward two-thirds or so 24′ of the plunger 24 is plain,but to the rear of this is a threaded section 24″ which terminates in aflange 27 and a plain end 28. Rotatably fitted in the rearward end ofthe body portion 12 is a dose setting collar 30 which is fixedlyconnected to a setting cylinder 32 the forward end of which is providedwith an externally directed ratchet surface 33 a which cooperates withan internally directed ratchet surface 33 b on the drive gear 34, asshown in FIG. 1 b. The ratchet mechanism allows relative ratchetingmovement of the dose setting collar 30 and the setting cylinder 32relative to the drive gear 34 in a dose setting direction but not in thereverse, dose expelling direction. As drawn, the dose setting directionis clockwise when viewed on the rearward end of the device. A torsionspring (35 is secured at its rearward end to the dose setting collar andat its forward end is anchored to be rotationally fixed with respect tothe main body 12. A trigger 36 is slidably mounted in said main bodyportion 12 and moveable against a spring bias from a forward position inwhich it locks the drive gear 34 against rotation and a rearwardposition in which the drive gear 34 is free to rotate.

In use of the metered dose setting drive mechanism, the required dose isdialled in by rotating the dose setting collar 30 by the required numberof clicks provided by the ratchet between the setting cylinder 32 andthe drive gear 34. During this setting routine, the drive sleeve 34 doesnot rotate, being kept still by the trigger 36 with the ratchet betweenthe sleeve 32 and the drive gear 34 allowing relative movement betweenthe two. Once the required number of clicks has been dialled in, theuser then inserts the needle into the injection site and pushes thetrigger 36 rearwardly to release the drive gear 34. The drive gear 34,now being free to rotate with the setting cylinder 32 and the settingcollar 30, is driven by the torsion spring anticlockwise by an amountequivalent to the angular amount dialled into the dose setting collar30. This rotary movement causes the plunger 24 to advance by virtue ofits threaded engagement with the inside of the drive collar 34. Furtherdetails of suitable arrangements are described in our U.S. Pat. No.6,104,380.

As noted, in the embodiment of this invention, the plunger is threadedalong only part of its length, the remainder being plain. Theconstruction and operation of this device will now be described. In FIG.1 a, the plunger 24 is shown in its retracted position prior to drivingthe rearward bung 18′ forwards. Slideably mounted in the end of thesetting cylinder 32 is a pushrod 38 with a cap 40. The pushrod 38 isdesigned to be a sliding fit within the setting cylinder 32. Releasingthe pushrod 38 and pushing it causes it to engage the plain end 28 ofthe plunger 24 so that the plunger can be moved longitudinally in areconstitution phase from the position shown in FIG. 1 a to that in FIG.2. Once fully pressed in, the cap 40 on the pushrod 38 may snap-fit intothe interior of the dose setting collar 30. As seen in FIG. 2, theforward movement is sufficient to move the rearward bung 18′ towards theforward bung 18″ to allow mixing of the therapeutic mixture. Thusinitially the rearward bung 18′ and the forward bung 18″, with thediluent liquid between them, move forward together a sufficient distancefor the forward bung 18″ to uncover the bypass 20, whereupon the forwardbung remains stationary, as the diluent liquid enters the forwardchamber, until the rearward bung abuts the forward bung.

A spring 42 acting between the rearward end of the setting cylinder 32and the flange 27 on the plunger 24 lightly biases the plunger to urgethe threaded portion 24″ on the plunger 24 into engagement with thecorresponding female thread in the drive sleeve 34. The pushrod 38 mayinterface with the setting sleeve in a bayonet lock type arrangement(not shown) requiring the cap 40 to be rotated before it can be pushedinto the shell 32, and also isolating the spring 42 and preventing thespring pushing the plunger onto the bung prior to use.

Following reconstitution, the device is made ready for injection bydialling in preset dose to prime the cartridge and to ensure thatthreads on the plunger and the drive collar are properly engaged.Thereafter the device may be used as a conventional pen injectiondevice.

The relaxed length of the spring 42 is selected so that it ceases toapply pressure to the plunger 24 shortly after the threads on theplunger 24 and the drive sleeve 34 have engaged. If required a removablesafety collar (not shown) may initially be releasably clipped around theexposed part of the pushrod 38 between the cap 40 and the dose settingcollar 30, to prevent premature mixing of the substances in the chambersof the cartridge.

1. An injection device configured for dispensing a substance from a dualor multi-chamber cartridge, said cartridge having a bung moveable in afirst reconstitution phase of movement and a second, dosing phase ofmovement, said device comprising: a body portion (12); a plunger (24)mounted in said body portion for longitudinal movement with respectthereto in a forward dispensing direction to co-operate in use with saidbung (18″ 18′); a plunger drive element (34) disposed adjacent saidplunger for driving said plunger; said plunger having a drive portion(24″) adapted drivingly to engage a complementary drive portion (33 a)on said drive element and adapted to impart dosing movement to saidplunger (24), said drive portion extending only partly along saidplunger to leave a forward non-drive portion; and a drive mechanism toapply a pre-selectable amount of angular movement to said plunger driveelement on activation thereof, said drive mechanism comprising: a usersuitable dose setting member rotatably mounted on said body portion toset a dose; a spring acting between said dose setting means and saidbody portion, said spring being strained to a variable extent dependingon movement of said dose setting member; a ratchet arrangement disposedbetween said dose setting member and said plunger drive element forallowing one way relative movement therebetween as said dose settingmember is rotated to set a dose; and a trigger member operable toprevent rotary movement of said drive element and releasable to allowsaid spring to rotate said dose setting member and said plunger driveelement by an amount corresponding to the set dose, whereby, during areconstitution phase, said plunger is moved longitudinally forward froma position with the non-drive portion adjacent said drive element butnot in driving engagement therewith, to bring its drive portion intodriving engagement with the drive portion on said drive element.
 2. Aninjection device according to claim 1, wherein said drive portions onsaid plunger drive element and said plunger are complementary threadeddrive portions.
 3. An injection device according to claim 2, whereinsaid plunger carries a male thread and said plunger drive elementincludes a bore having a female thread.
 4. An injection device accordingto claim 3, wherein said non-drive portion of said plunger comprises anon-threaded portion sized to be moveable freely through said plungerdrive element.
 5. An injection device according to claim 4, including amover element slideably moveable in said body portion and having anexternally accessible push region for being pushed to engage saidplunger and to move it to bring said complementary drive portions intodriving engagement.
 6. An injection device according to claim 4,including bias means for urging said plunger element towardscomplementary driving engagement with said plunger drive element.
 7. Aninjection device according to claim 3, including a mover elementslideably moveable in said body portion and having an externallyaccessible push region for being pushed to engage said plunger and tomove it to bring said complementary drive portions into drivingengagement.
 8. An injection device according to claim 3, including biasmeans for urging said plunger element towards complementary drivingengagement with said plunger drive element.
 9. An injection deviceaccording to claim 2, including a mover element slideably moveable insaid body portion and having an externally accessible push region forbeing pushed to engage said plunger and to move it to bring saidcomplementary drive portions into driving engagement.
 10. An injectiondevice according to claim 2, including bias means for urging saidplunger element towards complementary driving engagement with saidplunger drive element.
 11. An injection device according to claim 1,including a mover element slideably moveable in said body portion andhaving an externally accessible push region for being pushed to engagesaid plunger and to move it to bring said complementary drive portionsinto driving engagement.
 12. An injection device according to claim 11,including means for releasably preventing longitudinal movement of saidmover element.
 13. An injection device according to claim 12, whereinsaid mover element includes a cap element defining said push region,said cap element being adapted to engage in snap engagement an endregion of said injection device on completion of said reconstitutionmovement.
 14. An injection device according to claim 11, wherein saidmover element includes a cap element defining said push region, said capelement being adapted to engage in snap engagement an end region of saidinjection device on completion of said reconstitution movement.
 15. Aninjection device according to claim 1, including bias means for urgingsaid plunger element towards complementary driving engagement with saidplunger drive element.
 16. An injection device according to claim 15,wherein said bias means and said plunger are arranged such that saidplunger is isolated from the influence of said bias means followingdriving engagement between said complementary drive portions.
 17. Aninjection device according to claim 1, wherein said dose setting elementincludes a generally cylindrical portion surrounding at least part ofsaid plunger.
 18. An injection device configured for dispensing asubstance from a dual or multi-chamber cartridge, said cartridge havinga bung moveable in a first reconstitution phase of movement and asecond, dosing phase of movement, said device comprising: a bodyportion; a plunger mounted in said body portion for longitudinalmovement with respect thereto in a forward dispensing direction toco-operate in use with said bung; a plunger drive element disposedadjacent said plunger for driving said plunger; a drive mechanism toapply a pre-selectable amount of angular movement to said plunger driveelement on activation thereof; said plunger having a drive portionadapted drivingly to engage a complementary drive portion on saidplunger drive element and adapted to impart dosing movement to saidplunger, said drive portion extending only partly along said plunger toleave a forward non-drive portion; and a drive mechanism to apply apre-selectable amount of angular movement to said plunger drive elementon activation thereof, said drive mechanism comprising: a user suitabledose setting member rotatably mounted on said body portion to set adose; a spring acting between said dose setting means and said bodyportion, said spring being strained to a variable extent depending onmovement of said dose setting member; a ratchet arrangement disposedbetween said dose setting member and said plunger drive element forallowing one way relative movement therebetween as said dose settingmember is rotated to set a dose; and a trigger member operable toprevent rotary movement of said drive element and releasable to allowsaid spring to rotate said dose setting member and said plunger driveelement by an amount corresponding to the set dose, whereby, during areconstitution phase, said plunger is moved longitudinally forward froma position with the non-drive portion adjacent said drive element butnot in driving engagement therewith, to bring its drive portion intodriving engagement with the drive portion on said drive element.